As shown in FIG. 1, an auxiliary rule 10 of the prior art tile cutter is of an L-shaped construction and has a body 11 which is provided centrally along the direction of a longitudinal axis thereof with an elongate slot 12. The body 11 has an arm portion 13 extending vertically from the left end thereof. The arm portion 13 is provided on the right side thereof with a datum line 14 perpendicular to the longitudinal axis of the body 11. The auxiliary rule 10 is disposed pivotally in a long slot 16 of a gauge 15 by means of the body 11 and a bolt 17. The gauge surfaces located at the upper and the lower sides of the slot 16 are provided respectively with a scale. In operation, the bolt 17 is first loosened so as to adjust the position of the auxiliary rule 10. The tile which is intended to be cut is disposed such that the upper side of the tile is rested against the lower side of the gauge 15, and that the left side of the tile is rested against the datum line 14 of the arm portion 13 of the auxiliary rule 10. The cutting dimension of the tile is adjusted appropriately before the bolt 17 is tightened again. The operator uses his or her right hand to hold the tile 18 while he or she is doing the cutting with his or her left hand with which the grip rod 19 is pushed. As shown in FIG. 2, when the tile cutting device is used by a right-handed operator, the arm portion of the auxiliary rule should be located at the right side so as to facilitate the operator to push the grip rod with his or her right hand and to hold the tile with his or her left hand. It is conceivable that a tile cutter can sell better if it were equipped with an auxiliary rule suitable for use by both right-handers and left-handers.